1. Field of the Invention
Embodiments of the present invention generally relate to a system and method for sensing a position of an input object over a sensing region of a proximity sensing device.
2. Description of the Related Art
Input devices including proximity sensor devices, also commonly called touchpads or touch sensor devices, are widely used in a variety of electronic systems. A proximity sensor device typically includes a sensing region in which the proximity sensor device determines the presence, location and/or motion of one or more input objects, such as a finger. Proximity sensor devices may be used to provide interfaces for an electronic system. For example, proximity sensor devices are often used as input devices for larger computing systems, such as opaque touchpads integrated in, or peripheral to notebook or desktop computers. Proximity sensor devices are also often used in smaller computing systems, such as touch screens integrated in cellular phones. Proximity sensor devices are typically used in combination with other supporting components, such as display or input devices found in the electronic or computing system.
In some configurations, the proximity sensor devices are coupled to these supporting components to provide a desired combined function or to provide a desirable complete device package. Many commercially available proximity sensor devices utilize one or more electrical techniques to determine the presence, location and/or motion of an input object, such as a capacitive or a resistive sensing technique. Typically, a capacitive sensing type of proximity sensor device utilizes an array of sensor electrodes and traces to detect the presence, location and/or motion of an input object. A trace is an electronic component that connects a sensor electrode to the controlling electronics found in the proximity sensor device.
During the operation of a capacitive sensing device the presence of an input object over the sensing region of the proximity sensor device, which contains the sensor electrodes and their respective traces, the input object will interfere with the signal provided by the driven electrodes (i.e., transmitter electrodes) and also their respective traces (i.e., transmitter traces). Unfortunately, the coupling between the transmitter electrodes and the receiver electrodes is also affected by the interaction of the signal transmitted from the transmitter traces to the receiver electrodes. Thus, the interaction of an input object and the signal transmitted from the traces will cause an unwanted parasitic response. For example, a finger that is coupled to a particular sensor electrode is also likely to be coupled to traces that are connected to other sensor electrodes that are not positioned such that they will significantly interact with the input object. The controlling electronics in the proximity sensor device incorrectly interprets the coupling between the input object and the traces as a response at the other sensor electrodes that are not positioned to directly couple with the input object. This incorrect interpretation of a response created by the input object and the local traces is known as a parasitic response. The parasitic response causes the controlling electronics to incorrectly determine that one or more phantom input objects are interacting with the proximity sensor device, and affect the controlling electronics ability to determine the actual location of the actual input object.
Moreover, the closer the position of a trace is to a receiver electrode and also the greater the length of the traces used to interconnect the sensor electrodes to the computer system, the more susceptible the proximity sensor device is to a parasitic response. The width of a trace is typically designed to be wider as the length of the trace increases, for example, as the sensor electrode is farther away from the trace interconnecting region typically outside of the sensing region of the proximity sensor device. The parasitic response can thus vary from one type of trace to another, which will also adversely affect the reliability and accuracy of the data collected by the proximity sensing device.
Thus, there is a need for a method and an inexpensive electronic system that can facilitate reliable, consistent and accurate determination of the correct number of input objects and their position within the sensing region.